I have tested all the mixes, and tested various thicknesses of refractory backed up with perlcrete. If you could do centrifugal casting and get an even thickness of refractory, then perlcrete, then refractory, it is doable. It is doable in sheets, and even for oven doors (what I used it for). For a <2" round casting, good luck with that, you will get either an uninsulated unit, or a low mass unit, but not both.
My guess is that he has an uninsulated mass on the frankenweber, and that is certainly doable.